U.S. patent number 10,239,905 [Application Number 15/882,078] was granted by the patent office on 2019-03-26 for low temperature and efficient fractionation of lignocellulosic biomass using recyclable organic solid acids.
The grantee listed for this patent is The United States of America as Represented by the Secretary of Agriculture. Invention is credited to Liheng Chen, Roland Gleisner, Junyong Zhu.
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United States Patent |
10,239,905 |
Zhu , et al. |
March 26, 2019 |
Low temperature and efficient fractionation of lignocellulosic
biomass using recyclable organic solid acids
Abstract
Methods of fractionating lignocellulosic biomass using
hydrotropic sulfonic acids are provided. Also provided are methods
of forming lignin particles, furans, sugars, and/or lignocellulosic
micro- and nanofibrils from the liquid and solid fractions produced
by fractionation process. The fractionation can be carried out at
low temperatures with short reaction times.
Inventors: |
Zhu; Junyong (Madison, WI),
Chen; Liheng (Madison, WI), Gleisner; Roland (Jefferson,
WI) |
Applicant: |
Name |
City |
State |
Country |
Type |
The United States of America as Represented by the Secretary of
Agriculture |
Washington |
DC |
US |
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Family
ID: |
62977175 |
Appl.
No.: |
15/882,078 |
Filed: |
January 29, 2018 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180215774 A1 |
Aug 2, 2018 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62452282 |
Jan 30, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C12P
17/04 (20130101); D21B 1/38 (20130101); C12P
19/14 (20130101); C12P 19/04 (20130101); C12P
19/02 (20130101); C08B 37/0057 (20130101); D21B
1/08 (20130101); C07D 493/04 (20130101); C07G
1/00 (20130101); D21B 1/04 (20130101); D21D
5/005 (20130101); C08H 8/00 (20130101); D21B
1/02 (20130101); Y02W 30/642 (20150501); C12P
2201/00 (20130101); Y02W 30/64 (20150501) |
Current International
Class: |
C12P
17/02 (20060101); D21B 1/08 (20060101); C12P
19/04 (20060101); C12P 17/04 (20060101); D21B
1/02 (20060101); C08H 8/00 (20100101); C07G
1/00 (20110101); D21D 5/00 (20060101); D21B
1/04 (20060101); D21B 1/38 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Saidha; Tekchand
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority to U.S. provisional patent
application No. 62/452,282 that was filed Jan. 30, 2017, the entire
contents of which are hereby incorporated by reference.
Claims
What is claimed is:
1. A method for treating lignocellulosic biomass, the method
comprising: dispersing a lignocellulosic biomass in an aqueous
solution comprising a sulfonic acid, wherein the concentration of
the sulfonic acid in the solution is higher than its minimal
hydrotrope concentration; maintaining the solution at a temperature
and for a time sufficient to dissolve at least 10 wt. % of the
lignin in the lignocellulosic biomass; and separating the solution
and the dispersed lignocellulosic biomass into a spent acid
solution comprising dissolved lignin and a water-insoluble
cellulose-rich solids fraction comprising water-insoluble
lignocellulosic solid residues.
2. The method of claim 1, wherein the sulfonic acid in the solution
is p-toluenesulfonic acid.
3. The method of claim 1, wherein the temperature is no greater
than 100.degree. C. and the time is no greater than 300
minutes.
4. The method of claim 3, wherein the temperature is in the range
from 25.degree. C. to 85.degree. C., the time is in the range from
15 minutes to 180 minutes, and the concentration of sulfonic acid
in the solution is in the range from 15 wt. % to 85 wt. %.
5. The method of claim 1, wherein the temperature is no greater
than 25.degree. C. and the time is no greater than 24 hours.
6. The method of claim 1, wherein the lignocellulosic biomass
comprises wood chips, milled wood, commercial technical lignin, or
a combination thereof.
7. The method of claim 1, wherein the lignocellulosic biomass is a
hardwood and at least 10 wt. % of the lignin in the hardwood is
dissolved.
8. The method of claim 7, wherein the temperature is in the range
from 25.degree. C. to 85.degree. C., the time is in the range from
15 minutes to 180 minutes, and the concentration of sulfonic acid
in the solution is in the range from 15 wt. % to 85 wt. %.
9. The method of claim 1, wherein the lignocellulosic biomass is
softwood and at least 10 wt. % of the lignin in the softwood is
dissolved.
10. The method of claim 1, wherein the lignocellulosic biomass is
commercial technical lignin and the amount of the technical lignin
dissolved is at least 2 g/100 g solution.
11. The method of claim 1, further comprising fibrillating the
lignocellulosic biomass prior to dispersing the lignocellulosic
biomass in the aqueous solution comprising the sulfonic acid.
12. The method of claim 1, further comprising precipitating lignin
nanoparticles from the spent acid solution.
13. The method of claim 1, further comprising converting sugars
dissolved in the spent acid solution into furans and separating the
furans from the spent acid solution.
14. The method of claim 1, further comprising mechanically
fibrillating the lignocellulosic solid residues to form
lignocellulosic microfibrils, lignocellulosic nanofibrils, or a
combination thereof.
15. The method of claim 14, wherein the water-insoluble
cellulose-rich solids fraction comprises lignocellulosic solid
residues and lignocellulosic nanocrystals.
16. The method of claim 15, further comprising separating the
lignocellulosic solid residues from the lignocellulosic
nanocrystals.
17. The method of claim 1, further comprising converting the
water-insoluble lignocellulosic solid residues into sugars via
hydrolysis using enzymes or chemicals.
18. The method of claim 1, further comprising recycling the
sulfonic acid in the spent acid solution back into the aqueous
solution comprising the dispersed lignocellulosic biomass.
Description
FIELD OF THE INVENTIONS
The inventions described herein relate to the field of
fractionation of lignocellulosic plant biomass, such as wood
biomass, for value added utilizations.
BACKGROUND
The per capita demand for cellulosic fibers in textiles is expected
to increase from 3.7 to 5.4 kg in the next 15 years. With the
Earth's population estimated to grow from 6.9 to 8.3 billion in the
same time period, it is expected that cotton, a major source of
cellulosic fibers, will not meet market demand due to the estimated
production of only 3.1 kg per capita in 2030, based on anticipated
shrinkage of cotton growing area (Hauru et al. 2013). Therefore,
producing man-made cellulosic-based fibers, such as viscose,
cellulose acetate, etc., from dissolving pulp will be a necessary
alternative to make up this large market shortage of at least 1.7
kg per capita for native cellulosic fibers. Dissolving pulp fibers
are commercially produced using either sulfite pulping or hot-water
pre-hydrolysis coupled with kraft pulping, both developed in the
1950's. The main problems with sulfite pulping are chemical
recovery and environmental concerns due to SO.sub.2 air emissions.
The metal base in sulfite pulping, excepting magnesium, cannot be
recovered. Pre-hydrolysis with kraft pulping is very expensive in
terms of energy. Chemical recovery in kraft pulping is commercially
practiced using the Tomlinson recovery boiler, but is capital
intensive. The hemicellulosic sugars from hot-water pre-hydrolysis
are often discarded to save energy, which can create substantial
biochemical oxygen demand (BOD) problems.
Cellulose nanomaterials have attracted great attention recently for
their unique optical and mechanical properties (Moon et al. 2011;
Zhu et al. 2016). Most of the published research, however, has been
focused on cellulose nanomaterials produced using bleached fibers
that do not contain lignin. Lignin is relatively hydrophobic, which
can be beneficial for certain applications. Unfortunately, only a
few studies have reported the production of lignin containing
cellulose nanomaterials from commercial unbleached chemical pulps
using direct mechanical fibrillation, which is energy intensive and
does not produce surface functional groups which aid dispersion
(Rojo et al. 2015; Spence et al. 2010). A study on the production
of lignocellulose nanomaterials directly from wood is reported as a
patented process by American Process, Inc. at high temperatures
using an organic solvent solution of concentrated ethanol and
sulfur dioxide (Nelson et al. 2015).
Nano sized particles have attracted great interest due to their
large specific surface areas and shape dependent properties for a
variety of potential applications (Xia et al. 2009). Organic
nanoparticles (Kamaly et al. 2016; Mavila et al. 2016; Reisch and
Klymchenko 2016), especially those derived from biodegradable and
benign natural biopolymers, such as cellulose, chitin and DNA, are
more attractive from a sustainability point of view. Lignin, the
second most abundant natural polymer from a plant biomass cell
wall, has so far found limited economical utilization other than as
a boiler fuel through combustion in pulp mills (Duval and Lawoko
2014; Upton and Kasko 2016). With rapid advances in nanotechnology,
lignin, as a renewable and abundant biopolymer, has gained growing
interests in the nanotechnology field (Frangville et al. 2012; Nair
et al. 2014). Lignin nanoparticles (LNPs) have potential
applications in developing novel and biodegradable materials and
advancing biotechnologies (Jiang et al. 2013; Qian et al. 2014;
Richter et al. 2015; Ten et al. 2014).
The commercial applications of LNPs through industrial processing,
however, are impeded by the difficulties in economical production
from the plant cell wall. Almost all of the existing methods for
the production of LNPs use commercial technical lignin which
requires dissolution in solvents, such as ethylene glycol, acetone,
tetrahydrofuran (THF), or N,N-dimethylformamide (DMF), followed by
either acidic precipitation (Frangville et al. 2012; Richter et al.
2016), hexane precipitation (Qian et al. 2014), dialysis (Lievonen
et al. 2016), or atomization and drying (Ago et al. 2016). The use
of organic solvents such as ethylene glycol and THF is an
environmental concern and increases LNP cost for solvent recovery.
Also, the LNP properties are affected by the original feed lignin
sources generated from various pulping processes.
Hydrotropic chemistry using concentrated aromatic salts as solvents
for solubilizing a range of hydrophobic compounds was discovered in
1916 by Neuberg. Its application for fractionation of
lignocellulosic biomass was first practiced by McKee (McKee 1943).
For pulping poplar using 30-40 weight percent (wt %) aqueous sodium
xylenesulfonate liquor, a reaction of temperature of 150.degree. C.
for 11-12 hr was needed to obtain a cellulosic solids yield of 52%
(McKee 1946). There are many hydrotropic agents that can be used to
dissolve lignin (Procter 1971). The most used salts were sodium
salicylate and xylenesulfonate, cumenesulfonate. Sodium
xylenesoulfonate was found to have very strong hydrotropic activity
at 30 wt % and only required a 3-time dilution to lose its
hydrotropic properties and, thus, precipitate lignin (Robert 1955).
There have been numerous studies on hydrotropic pulping since its
invention (Gromov and Odincov 1959; McKee 1954; Procter 1971)
including using additives (Kalninsh et al. 1967; Nelson 1978).
However, the processes were never commercialized due to low pulp
yields, poor pulp mechanical properties, and very long cooking
times. Moreover, the processes were not suitable for pulping
softwoods, due to insufficient delignification (Procter 1971).
Recently, hydrotropic pulp was found to be enzymatically digestible
for sugar production (Korpinen and Fardim 2009). To reduce reaction
time, additives such as formic acid and hydrogen peroxide were used
(Gabov et al. 2013). A recent study included the characterization
of lignin from modified hydrotropic processes used for subsequent
sugar production (Gabov et al. 2014). The utilization of
hydrotropic lignin, however, has remained limited (Kalninsh et al.
1962; Procter 1971).
SUMMARY
Methods of treating lignocellulosic biomass to fractionate the
lignocellulosic biomass and/or to dissolve lignin are provided.
One embodiment of a method for treating lignocellulosic biomass
includes dispersing a lignocellulosic biomass in an aqueous
solution comprising a sulfonic acid, such as p-toluenesulfonic
acid. The concentration of the sulfonic acid in the solution is
higher than its minimal hydrotrope concentration so that lignin in
the lignocellulosic biomass is dissolved. The solution is
maintained at a temperature and for a time sufficient to dissolve
at least 10 wt. % of the lignin in the lignocellulosic biomass. The
solution and the dispersed lignocellulosic biomass can then be
separated into a spent acid solution comprising dissolved lignin
and a water-insoluble cellulose-rich solids fraction referred to as
water-insoluble lignocellulosic solid residues (LCSR).
Optionally, the spent acid solution and/or the water-insoluble
lignocellulosic solid residues can then the further processed. For
example, the spent acid solution can be further processed by
precipitating out lignin nanoparticles and/or by converting
dissolved sugars into furans, which can be separated from the spent
acid solution. The lignocellulosic solid residues can be further
processed into lignocellulosic microfibrils, lignocellulosic
nanofibrils, or a combination thereof via mechanical fibrillation
and/or by converting them into sugars via hydrolysis.
Other principal features and advantages of the invention will
become apparent to those skilled in the art upon review of the
following drawings, the detailed description, and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Illustrative embodiments of the invention will hereafter be
described with reference to the accompanying drawings, wherein like
numerals denote like elements.
FIG. 1 is a flow chart showing one embodiment of a wood processing
method that includes a lignocellulosic biomass fractionation using
sulfonic acid hydrotropes.
FIG. 2A is a graph of L.sub.R, the fractions of lignin retained on
the water insoluble solids of Example 2. FIG. 2B is a graph of
X.sub.R, the fractions of xylan retained on the water insoluble
solids of Example 2.
FIG. 3A is a graph of the cellulose enzyme digestibility for NE222
fractionated solids that were fractionated using a p-TsOH
concentration of 75 wt % at 65.degree. C. for different times. FIG.
3B is a graph of the cellulose enzyme digestibility for NE222
fractionated solids that were fractionated using a p-TsOH
concentration of 70 wt % for 35 min at different temperatures.
FIG. 4A is an atomic force microscope (AFM) image of separated LCNC
particles for sample P85T80t20 from Example 7. FIG. 4B is an AFM
image of separated LCNC particles for sample P80T80t20 from Example
7. FIG. 4C is an AFM image of separated LCNC particles for sample
P65T80t20 from Example 7.
FIG. 5 shows the AFM height measured distributions for samples
P85T80t20, P80T80t20, and P65T80t20 from Example 7.
FIG. 6A is an AFM image of separated LCNF particles for sample
P50T80t20 from Example 8. FIG. 6B is an AFM image of separated LCNF
particles for sample P65T80t20 from Example 8. FIG. 6C is an AFM
image of separated LCNF particles for sample P80T80t20 from Example
8.
FIG. 7 is a graph showing AFM height measured distributions for
LCNF samples P80T80t20, P65T80t20, and P50T80t20 from Example
8.
FIG. 8A is an AFM image of the LCNFs from P50T80t20 of Example 8
after one pass through the chamber of a microfluidizer. FIG. 8B is
an AFM image of the LCNFs of Example 8 after three passes through
the chamber of a microfluidizer. FIG. 8C is an AFM image of the
LCNFs of Example 8 after five passes through the chamber of a
microfluidizer. FIG. 8D is an AFM image of the LCNFs of Example 8
after seven passes through the chamber of a microfluidizer. FIG. 8E
is an AFM image of the LCNFs of Example 8 after nine passes through
the chamber of a microfluidizer.
FIG. 9 shows the AFM height measured distributions for the LCNFs of
FIGS. 8A-8E.
FIG. 10A is an image of the whisker-like cellulose nanofibrils of
Example 9. FIG. 10B is an enlarged image of the whisker-like
cellulose nanofibrils of Example 9.
FIG. 11 is another image of the whisker-like cellulose nanofibrils
of Example 9.
FIG. 12 is a graph showing lignin particle sizes measured by
dynamic light scattering in a spent liquor at different acid
dilution ratios, as described in Example 10.
FIG. 13 is a graph of conductivity measurements versus
concentration for aqueous p-TsOH solutions, as described in Example
10.
FIG. 14 is an AFM topographic image of the lignin particles of
Example 11 deposited on a fresh mica sheet.
FIG. 15 is a graph showing the height profile of the lignin
particles of FIG. 14.
FIG. 16A is an AFM image of lignin particle aggregates in a
supernatant centrifuged at a centrifuge speed of 3000 g with a
lateral size of approximately 600 nm, as described in Example 11.
FIG. 16B is an AFM image of small lignin particle aggregates in a
supernatant centrifuged at a centrifuge speed of 10000 g. FIG. 16C
is an AFM image of lignin particle aggregates in a supernatant
centrifuged at a centrifuge speed of 15000 g
FIG. 17 is a graph of AFM height measurements of the LCNF samples
of FIGS. 16A-16C.
FIG. 18 is a graph of LNP particle size measured by dynamic light
scattering as a function of centrifugation speed.
FIG. 19A is a graph of LNP particle size measured by dynamic light
scattering as a function of dilution speed for the LNPs of Example
12. FIG. 19B is an AFM height measurement of the LNPs of FIG. 19A
at different dilution rates.
FIG. 20A is an AFM image of lignin aggregates formed using a
dilution time/min of 0.05, as described in Example 12. FIG. 20B is
an AFM image of lignin aggregates formed using a dilution time/min
of 1.5. FIG. 20C is an AFM image of lignin aggregates formed using
a dilution time/min of 240.
FIG. 21A is a graph of LNP particle size and zeta potential for the
LNPs of Example 12 as a function of solution pH. FIG. 21B is a
graph of AFM height measurements for the LNPs of FIG. 21A at
different pH values.
FIG. 22A is an AFM image of the LNCs of Example 12 at a solution pH
of 11.5. FIG. 22B is an AFM image of the LNCs of Example 12 at a
solution pH of 7.5. FIG. 22C is an AFM image of the LNCs of Example
12 at a solution pH of 5.4.
FIG. 23A is a graph of LNP particle size and zeta potential for the
LNPs of Example 12 as a function of NaCl concentration. FIG. 23B is
a graph of AFM height measurements for the LNPs of FIG. 23A at
different NaCl concentrations.
FIG. 24A is an AFM image of the LNPs of Example 12 for an NaCl
concentration of 10 mM. FIG. 24B is an AFM image of the LNPs of
Example 12 for an NaCl concentration of 33 mM. FIG. 24C is an AFM
image of the LNPs of Example 12 for an NaCl concentration of 5
mM.
FIG. 25 is a graph of LNP particle size and zeta potential for the
LNPs of Example 12 as a function of dissolved lignin content.
FIG. 26 is a graph of the colloidal stabilities of LNPs in a
supernatant from a centrifuge and in a suspension of re-suspended
precipitates over a period of two weeks.
FIG. 27 is a graph of the zeta potential of LNPs in a supernatant
from a centrifuge and in a suspension of re-suspended precipitates
over a period of two weeks.
FIG. 28A is an AFM image of the LNPs in a supernatant at t=0 hours.
FIG. 28B is an AFM image of the LNPs in a supernatant at t=336
hours, as described in Example 14.
FIG. 29 is a graph of AFM height measurements of the samples of
FIGS. 28A and 28B.
FIG. 30A is an AFM image of LNPs from a suspension of re-suspended
precipitates. FIG. 30B is an AFM image of LNPs from a suspension of
re-suspended precipitates from a centrifuge at t=0.
FIG. 31 is a graph of AFM height measurements of the LNPs in FIG.
30A at t=0 and in FIG. 30B at t=336 hours.
FIG. 32A shows an optical micrograph image (left panel) and a
scanning electron microscope (SEM) image (right panel) of MDF
fibers before delignification. FIG. 32B shows an optical micrograph
(left panel) and an SEM image (right panel) of MDF fibers after
delignification.
FIG. 33A shows and optical micrograph (left panel) and an SEM image
(right panel) of delignified and refined MDF fibers at a Canadian
Standard Freeness (CSF) of 650 mL. FIG. 33B shows an optical
micrograph (left panel) and an SEM image (right panel) of
delignified and refined MDF fibers at a Canadian Standard Freeness
(CSF) of 450 mL.
FIG. 34A is a graph of the tensile index as a function of CSF for a
birch MDF sheet. FIG. 34B is a graph of the failure strain as a
function of CSF for a birch MDF sheet.
FIG. 35A is a graph of the solubility of alkali technical lignin as
a function of p-TsOH concentration. FIG. 35B is a graph of the
solubility of alkali technical lignin as a function of solution
temperature.
FIG. 36A is an AFM image of precipitated LNPs from sample P40T35.
FIG. 36B is an AFM image of precipitated LNPs from sample P50T65.
FIG. 36C is an AFM image of precipitated LNPs from sample
P55T80.
FIG. 37 is a graph of AFM height measurements of the samples of
FIGS. 36A-36C.
FIG. 38A is the first part of Table 1 from Example 2. FIG. 38B is
the second part of Table 1 from Example 2. Table 1. Shows the
chemical compositions of p-TsOH fractionated poplar NE222 samples
under different treatment conditions. The numbers in the
parentheses are component yields based on component in the
untreated NE222..sup.1 (Pxx, Txx, txx) stands for p-TsOH
concentration in wt %, reaction temperature in .degree. C. and
reaction duration in min..sup.2 Yields are based on xylan content
in NE222. HMF in spent liquors were not detectable.
DETAILED DESCRIPTION
Various embodiments of the inventions described herein are based,
at least in part, on the discovery that certain organic solid acids
have hydrotropic properties, and are capable of efficiently
solubilizing hydrophobic lignin at low temperatures (below the
boiling point of water) in a short period of time. As such, a
low-energy, low-cost and efficient lignocellulosic biomass
fractionation process can be carried out using these easily
recyclable organic solid acids, which include p-toluenesulfonic
acid (p-TsOH), in aqueous solution, at low temperatures and
atmospheric pressures. The fractionation produces a solid fraction
that contains mainly cellulose and some hemicelluloses and a liquid
fraction that contains dissolved lignin and some hemicellulosic
sugars. The solid fraction can be used with or without bleaching to
produce wood fibers, and/or cellulose micro- or nanomaterials,
and/or sugars (through hydrolysis), and/or valuable chemicals, such
as furfural. The cellulose micromaterials and nanomaterials include
lignocellulosic micro-fibrils (LCMFs) or lignocellulosic
nano-fibrils (LCNFs) with controllable lignin contents on their
surfaces (e.g., coated via precipitation) or in their cellulosic
matrices (containing native lignin) from the fractionated solids.
The solubilized lignin in the liquid fraction can be separated as
lignin nanoparticles through the precipitation of solubilized
lignin by diluting the spent acid solution with water to a
concentration below the minimal hydrotrope concentrations (MHC).
The obtained lignin nanoparticles (LNPs) comprise oblate spheroids
with tunable morphology and surface properties. Some embodiments of
the LNPs have diameters ranging from, for example, 150.about.3000
nm and thicknesses ranging from, for example, 3.about.50 nm. The
properties of the lignin LNPs can be tailored by controlling the
pretreatment conditions of the biomass and the diluting factors of
the spent acid solutions, as illustrated in the Examples.
Lignocellulosic Biomass:
As used herein, the term lignocellulosic biomass refers to
materials from plant cell wall that primarily includes lignin and
hemicelluloses, as well as cellulose. Lignocellulosic biomass may
be, for example, wood, grasses, and agriculture crop stems or
stalks. Wood biomass can be a hardwood or a softwood or a mixture
thereof. The wood may be provided in milled or chip form. However,
for the production of wood fibers, wood chips may be more
suitable.
Lignocellulose Nanocrystals (LCNCs):
As used herein, the term LCNC refers to elongated rod-like
crystalline lignin-containing cellulose nanoparticles. LCNCs
comprise cellulose chains produced from lignocellulosic biomass via
fractionation. LCNCs can be in the form of a single cellulose
crystallite or a bundle of cellulose crystallites, and may or may
not contain hemicelluloses. LCNCs are generally characterized by
lengths in the range from about 60 to about 1000 nm; widths in the
range from about 5 to about 50 nm; and corresponding aspect ratios
in the range from about 1 to about 200.
Lignocellulose Nanofibrils (LCNFs):
As used herein, the term LCNF refers to long flexible fiber-like
lignin-containing cellulose nanoparticles. LCNFs can be branched or
unbranched and can take the form of a network of flexible
fiber-like nanoparticles. LCNFs comprise cellulose, hemicellulose,
and lignin. The fiber-like lignocellulose particles are generally
characterized by lengths in the range from about 100 to about 5,000
nm; widths in the range from about 5 to about 200 nm; and
corresponding aspect ratios in the range from about 2 to about
1,000.
Lignocellulose Fibers (LCFs):
As used herein, the term LCF refers to lignin-containing cellulose
particles. LCFs comprise cellulose, hemicellulose, and lignin. LCFs
are generally characterized by lengths in the range from about 0.05
to about 3 mm; widths in the range from about 5 to about 50 .mu.m;
and corresponding aspect ratios in the range from about 2 to about
500.
Lignocellulose Microfibers (LCMFs):
As used herein, the term LCMF refers to lignin-containing cellulose
microparticles. LCMFs comprise cellulose, hemicelluloses, and
lignin. LCMFs are characterized by lengths in the range from about
5 to about 100 .mu.m; widths in the range from about 0.1 to about
10 .mu.m; and corresponding aspect ratios in the range from about 2
to about 500.
Lignocellulosic Solid Residues (LCSR):
As used herein, the term LCSR refers to a solid material composed
of LCFs, LCMFs, or a combination thereof. In the present methods,
LCSRs are part of the solid material remaining after the biomass
fractionation.
Lignin Nanoparticles (LNPs):
As used herein, the term LNP refers to lignin nanoparticles. LNPs
can be in the form of single lignin macro molecule or aggregates of
lignin macro molecules. LNPs are generally characterized by
dimensions in the range from 1 nm to 10 .mu.m (e.g., from 10 nm to
500 nm) and may have an oblate spheroid shape.
The lignocellulosic biomass fractionation methods utilize sulfonic
acids, such as methenesulfonic acid, and, in some embodiments,
aromatic sulfonic acids, such as p-toluenesulfonic acid,
benzenesulfonic acid, xylenesulfonic acid, and mixtures of two or
more thereof, or mixtures of one or more thereof with their
salts.
One aspect of the present invention uses a concentrated organic
sulfonic acid, rather than, or in addition to, sulfonic (aromatic)
salts, to solubilize lignin for wood fractionation. With sulfonic
aromatic acids, the process can be conducted at low temperatures
using a very short reaction time. By way of illustration, various
embodiments of the lignocellulosic biomass fractionation are
carried out at temperatures of no greater than 100.degree. C. This
includes embodiments of the lignocellulosic biomass fractionation
that are carried out at temperatures of no greater than 90.degree.
C. and further includes embodiments of the lignocellulosic biomass
fractionation that are carried out at temperatures of no greater
than 80.degree. C. For example, the lignocellulosic biomass
fractionation can be carried out at temperatures in the range from
30.degree. C. to 85.degree. C., including temperatures in the range
from 50.degree. C. to 85.degree. C., and further including
temperatures in the range from 60.degree. C. to 80.degree. C.
However, temperatures outside of these ranges can be used,
depending on the desired degree of lignin dissolution. For example,
the lignocellulosic biomass can simply be soaked in the
lignocellulosic biomass solution at ambient temperatures (e.g.,
temperatures no greater than 25.degree. C.) overnight (e.g., for a
period of less than 24 hours). By way of further illustration,
various embodiments of the lignocellulosic biomass fractionation
can be completed in a reaction time of 5 hours or less. This
includes embodiments of the lignocellulosic biomass fractionation
that are completed in a reaction time of 4 hours or less, 3 hours
or less, 2 hours or less, and 1 hour or less. For example, the
lignocellulosic biomass fractionation can be carried out for a
reaction time in the range from 15 minutes to 90 minutes, including
reaction times in the range from 20 minutes to 60 minutes. However,
reaction times outside of these ranges can be used, depending on
the desired degree of lignin dissolution. As used herein, the
reaction time refers to the time between the onset of the
solubilization of the lignin in the biomass by the sulfonic acid
and the cessation of the lignin solubilization when the sulfonic
acid concentration in the fractionation solution is brought below
its minimal hydrotrope concentration. By way of illustration, the
solubilization of lignin using p-TsOH can be terminated by
decreasing the acid concentration to below about 11.5 wt. %.
In the lignocellulosic biomass fractionation solution, the sulfonic
acid has a concentration above its minimum hydrotrope
concentration, so that it solubilizes lignin, which is hydrophobic,
in the fractionation solution. Generally, the sulfonic acid has a
concentration that is significantly greater than the minimum
hydrotrope concentration in order to enhance lignin solubilization.
By way of illustration, in various embodiments of the
lignocellulosic biomass fractionation method, the fractionation
solution has a sulfonic acid (for example p-TsOH) concentration of
at least 15% (or above MHC). This includes embodiments of the
methods in which the fractionation solution has a sulfonic acid
concentration of at least 50%, at least 60%, at least 65%, at least
70%, at least 75%, and at least 80%. For example, sulfonic acid
concentrations in the range from about 50% to about 85%, including
in the range from about 65% to about 80%, can be used. However,
concentrations outside of these ranges can be used, depending upon
the desired degree of lignin dissolution.
The lignocellulosic biomass fractionation process can solubilize
the majority of the lignin in a lignocellulosic biomass sample
without the need for an initial pulping to reduce the lignin
content prior to the sulfonic acid treatment. In various
embodiments of the lignocellulosic biomass fractionations, at least
10% of the lignin in the biomass is solubilized during the
fractionation. This includes embodiments of the fractionations that
solubilize at least 45%, at least 50%, at least 55%, at least 60%,
at least 65%, at least 70%, at least 75%, at least 80%, and at
least 90% of the lignin in the biomass. However, percentages of
lignin solubilization outside of these ranges can also be achieved.
The solubilization of the lignin can also be quantified in terms of
grams of lignin dissolved per 100 g of solution. In some
embodiments of the lignocellulosic biomass fractionation, at least
2 g lignin/100 g of solution is dissolved.
One aspect of the invention provides a low temperature and ambient
pressure wood processing method that includes lignocellulosic
biomass pre-treatment, followed by the lignocellulosic biomass
fractionation and, optionally, post-fractionation processing that
can be carried out for producing fibers, and/or LCNF or LCMF,
and/or sugars, and/or LNP with recovery of acid, as schematically
shown in FIG. 1. In a lignocellulosic biomass pre-treatment step,
lignocellulosic biomass 102, such as wood, is size-reduced 104
using, for example, low mechanical energy input disk milling
conducted at temperatures above lignin glass transition
temperature. Additionally, lignocellulosic biomass, such as wood
chips, can be fibrillated using, for example, mechanical
fibrillation, in order to increase exposed lignin at the fiber
surfaces prior to lignocellulosic biomass fractionation. Another
pre-treatment step that can be included in the process is
prehydrolysis using hot water to improve hemicellulose removal and
delignification. The size-reduced, fibrillated, and/or
prehydrolyzed lignocellulosic biomass is then fractionated 106
using a sulfonic aromatic acid, such as p-TsOH, as a hydrotrope 108
for the lignin in the biomass at a low temperature (for example,
approximately 80.degree. C. or lower) for a short time (e.g., 20
minutes to one hour). After subsequent filtration and, optionally,
washing 110, the spent acid solution from the lignocellulosic
biomass fractionation 106 can be cycled back to the fractionation
and directly reused 112. After several runs, dissolved solids, such
as lignin and sugars, accumulate in the spent acid solution. These
may be removed to further reuse the acid. Dissolved lignin in the
filtrate can be easily removed by precipitation initiated through
dilution with water 114. The diluted spent liquor can then be
reconcentrated to convert dissolved sugars, such as xylose, into
furans, such as furfural, through dehydration (e.g., evaporation)
116 using the sulfonic aromatic acid in the liquor as a catalyst.
Reconcentration can also facilitate the removal of excess sulfonic
aromatic acid 118 from the system through crystallization 116 when
desirable. The furans 122 can be separated through distillation and
dehydration 120. The remaining acid solution can then be cycled
back to reused in the lignocellulosic biomass fractionation 106.
The separated and subsequently washed water-insoluble solids
contain lignocellulosic solid residues (LCSRs), and lignocellulosic
nanocrystals (LCNC). Optionally, the LCNCs can be separated from
the LCSRs by dialysis. The LCSR, with or without separating LCNC,
can be used for producing chemical pulp fibers such as dissolving
pulps 124 after bleaching 126, lignocellulose micro and/or
nanofibrils (LCMF and/or LCNF) 128 with mechanical fibrillation
130, or sugars 132 through (enzymatic) hydrolysis 134.
Another aspect of the inventions provides methods for the
production of LCNCs, LCNFs, LCMFs, and/or wood fibers from
fractionated water insoluble solids, as described above and
illustrated in FIG. 1. As illustrated in Example 7, the relative
amount of LCNFs or LCMFs produced can be controlled by the severity
of biomass fractionation. As illustrated in Example 8, low severity
fractionation conditions tend to favor the production of long
LCNFs.
Another aspect of the inventions provides methods for the
production of LNPs with controllable sizes and shapes directly from
the spent liquor from the biomass fractionation simply by
precipitation after water dilution, as illustrated in FIG. 1.
Processing conditions that can be used to control the size and
morphology of the LNPs include the rate at which the spent
fractionation solution is diluted and the severity of the biomass
fractionation reaction conditions. The pH of the solution can also
be used to tailor LNP size, whereby changing the pH of the spent
liquor from the biomass fractionation to a low value (e.g.,
.ltoreq.3) or a high value (e.g., .gtoreq.10) results in a larger
LNP size.
Another aspect of the inventions provides methods for the
production of valuable chemicals, such as furans (e.g., furfurals),
from the dissolved sugars, as illustrated in FIG. 1.
As used in this disclosure, any concentrations that are provided as
a percentage (%) refer to a weight percentage (wt %), unless
otherwise indicated.
EXAMPLES
Materials Used
p-TsOH was purchased from Sigma-Aldrich (St. Louis, Mo.). Poplar
NE-222 (Populus deltoides Bartr. ex Marsh.times.P. nigra L.) were
harvested from Hugo Sauer Nursery in Rhinelander, Wis., USA, and
provided by the US Forest Service, Northern Research Station. The
NE222 logs were debarked and chipped at the US Forest Service,
Forest Products Laboratory. Douglas-fir (Pseudotsuga menziesii)
wood chips were collected by Weyerhaeuser Company from a pulp mill
in Washington State. The NE222 and Douglas-fir wood chips were
ground to a 20-mesh size using a Wiley mill.
White birch logs were obtained from the US Forest Service,
Rhinelander Experimental Forest, Northern Research Station. The
logs were harvested in February 2016 and had breast height diameter
of 6-8 inches. The logs were peeled in March 2016 and immediately
chipped at the US Forest Service, Forest Products Laboratory. The
chips were screened using 11/4'' square holes. Oversized chips were
re-chipped to increase recovery.
Another softwood feedstock originated from Timber Products in
Yreka, Calif. The feedstock are residuals from a veneer operation
and comprise predominantly ponderosa pine with a small percentage
of sugar pine. During veneer processing, all logs were debarked.
On-spec logs were peeled for veneer, while defective logs were sent
to the byproduct chipper. After veneer peeling, the residual bolts
were chipped in a whole log chipper. The outputs of the two chipper
lines were then mixed and screened. The undersized particles were
sent to particle board production, while the oversized particles
were re-chipped. The Timber Products specification for the
resulting residual chips is less than 1% bark.
Example 1: Wood Fractionation Using a Concentrated p-TsOH
Solution
Concentrated p-TsOH aqueous solutions at desired mass
concentrations were prepared using de-ionized (DI) water. For
studies using Wiley milled poplar and Douglas-fir wood particles,
50 mL of a prepared acid solution was added into a 150 mL flask and
heated to the preset reaction temperature on a heating plate. A 5 g
oven dry (OD) quantity of wood particles was transferred into the
flask. The flask was then placed on a shaker at 200 rpm. At the end
of the preset reaction time (between 5-60 min), the reaction was
terminated by adding an appropriate amount of DI water to dilute
the concentration down to 40 wt %. The solids were separated from
the liquor using vacuum filtration. The filtrate was collected to
produce LNP through dilution. The solids were thoroughly rinsed
using DI water until the pH of the rinse filtrate did not change.
The final rinsed solids were collected for compositional
analyses.
Example 2: Fractionated Solids of NE222
The chemical compositions of the original, as well as the
chemically fractionated solids of NE222, were analyzed by the
Analytical Chemistry and Microscopy Lab (ACML) at the US Forest
Service, Forest Products Lab, as described previously (Davis 1998;
Luo et al. 2010). As listed in Table 1, FIGS. 38A and 38B,
concentrated p-TsOH solution was able to solubilize a substantial
(up to 90.7%) amount of poplar NE222 (hard wood) lignin using a
very short reaction time of approximately 30 min at a temperature
80.degree. C. or lower. This amount of lignin removal is equivalent
to chemical pulping that is often conducted at temperatures of
170.degree. C. for 2 hours with fairly high alkali loadings of
approximately 25% on wood. Dissolution of xylan was also
substantial. Glucan loss, however, was minimal, especially at a
temperature of 65.degree. C. or lower. Using an extended reaction
time of 60 min or longer can compensate for reduced reaction
severity at low temperatures, e.g., 65.degree. C., to achieve
improved lignin and hemicellulose dissolution while maintaining a
high glucan yield. Lignin condensation occurred at 80.degree. C.
with reaction times of 35 min or longer. To achieve desired
fractionation, the reaction severity can be adjusted. This is
demonstrated in Eqs. (1a, b) and (2a, b). This is important to the
production of pulp fibers, and especially for dissolving pulp
fibers which require high cellulose yield, good strength, and
minimal lignin and hemicellulose content.
.theta.'.theta.'.times..theta.'.theta.'.times..times..times..function..al-
pha.''.beta.'.times..times..times..theta..theta..times..theta..theta..time-
s..times..times..function..alpha..beta..times..times..times..times.
##EQU00001## where L.sub.R and X.sub.R are fractions of lignin and
xylan retained on the water insoluble solids (WIS), respectively.
.theta.' and .theta. are the fractions of bulk fast solubilization
lignin and xylan, respectively, .theta.'.sub.R or .theta..sub.R are
the fractions of unsolubilized residue lignin and xylan, f' or f
are the ratio of lignin or xylan solubilization between the slow
and bulk fast lignin or xylan, .alpha.', .alpha. and .beta.',
.beta. are adjustable parameters, E' and E are activation energy, R
is the universal gas constant (8.314 J mol.sup.-1 K.sup.-1), T is
temperature in kelvins, C is initial p-TsOH concentration in mol
l.sup.-1, and t is dissolution time in min.
Eqs. (1) and (2) fit to the experimental data very well, as shown
in FIGS. 2A and 2B. Furthermore, the dissolved carbohydrates in the
spent liquor were mainly in the form of monomeric sugars.
Degradation of xylose to furfural was minimal, less than 2% for
most runs due to the rapid and low-temperature p-TsOH fractionation
(Table 1 in FIG. 38A and FIG. 38B). Total xylan recovery from both
the retained xylan and the dissolved xylose (not including
oligomeric xylose in the spent liquor) were near 90% based on xylan
content in untreated poplar NE222. Acetic acid concentration in the
spent liquor was very low, at less than 1.5 g/L. These data
demonstrate that p-TsOH fractionation can also efficiently recover
hemicellulosic sugars.
Example 3: Fractionated Solids of Douglas-Fir
Fractionations were also carried out for Douglas-fir (softwood) as
listed in Table 2. p-TsOH was less effective in solubilizing
softwood lignin. A maximum of approximately 60% of Douglas-fir
lignin was solubilized using a p-TsOH concentration of 80 wt % for
20 min at 80.degree. C. An extended reaction time of 60 min caused
lignin condensation, and slightly increased the residual lignin in
the solids.
TABLE-US-00001 TABLE 2 Chemical compositions of p-TsOH fractionated
Douglas-fir solids under different treatment conditions. The
numbers in the parentheses are component yields. Solids yield
Glucan Xylan Mannan Lignin Douglas-fir.sup.1 (%) (%) (%) (%) (%)
untreated 100 34.3 7.2 7.7 31.0 P70T80t20 70.1 52.0 (106.4) 3.8
(37.3) 6.2 (56.0) 32.6 (73.5) P75T65t60 65.1 58.9 (111.9) 3.9
(35.1) 7.0 (58.7) 31.6 (66.2) P75T80t20 64.4 48.3 (90.7) 3.3 (29.6)
6.0 (49.6) 30.7 (63.7) P80T80t20 56.8 54.4 (90.1) 3.3 (26.3) 5.5
(40.7) 25.2 (46.1) P80T80t35 53.4 55.4 (86.4) 2.5 (18.9) 5.0 (35.1)
24.9 (42.8) P80T80t60 53.5 62.2 (97.1) 2.7 (19.8) 5.0 (34.4) 26.3
(45.3) .sup.1(Pxx, Txx, txx) stands for p-TsOH concentration in wt
%, reaction temperature in .degree. C. and reaction duration in
min.
Example 4: Sugar Production from Fractionated Solids
The fractionated solids of NE222 were found to be enzymatically
digestible. Therefore, the present methods using aromatic acids can
be applied for sugar/biofuel production from lignocellulosic
biomass using very low temperatures and at atmospheric pressure
with short reaction times. When enzymatic hydrolysis was conducted
using a commercial cellulase (CTec3) loading of 20 FPU/g glucan in
acetate buffer of pH 5.5, cellulose enzymatic digestibility of over
90% was achieved, as shown in FIGS. 3A and 3B, for substrates
produced at the more severe conditions, such as P75T65t35,
P75T65t60, and P70T80t20. ((Pxx, Txx, txx) stands for p-TsOH
concentration in wt %, reaction temperature in .degree. C. and
reaction duration in min.)
Sugar production from fractionated Douglas-fir softwood was also
carried out, but with slightly poorer performance compared with
that from NE222.
Solubilized sugars in the spent acid solution, mainly
hemicellulosic sugars, can be converted into furan, as discussed in
Example 2 (Table 1 in FIGS. 38A and 38B).
Example 5: Dissolving Pulp Fiber Production from Poplar Wood
The fractionated solids have the potential for wood fiber
production, especially dissolving grade pulp fibers, due to the
substantial removal of hemicelluloses by the acid. One of the key
measures of dissolving pulp is the pulp viscosity or DP. A separate
set of fractionation experiments were conducted. Pre-hydrolysis
using hot-water (HW) at 170.degree. C. for 50 min (corresponding to
a P-factor of 500) was applied to poplar wood chips to improve
hemicellulose removal and delignification. Wood chips were used in
these experiments, since Wiley milling shortens wood tracheid and
therefore is not suitable for fiber production. The HW
prehydrolyzed wood chips were then fractionated using a p-TsOH
solution at 80 wt % concentration at 80.degree. C. for 20 min based
on the results shown in Table 1, FIGS. 38A and 38B. It was found
that HW treatment did not improve lignin solubilization (Table 3).
An 8-inch hand-driven disk mill (Andritz Sprout-Bauer Refiner,
Springfield, Ohio) was also used to fiberize the wood chips to
improve delignification in the subsequent treatment, with and
without HW treatment, as shown in Table 3.
HW prehydrolysis, when applied alone, was relatively effective in
solubilizing hemicelluloses (Table 3). When milling was applied,
both the HW and non-HW samples behaved similarly; both allowed
significant delignification and both types had similar
hemicellulose contents (comparing Mill+P80T80t20 with
HW+Mill+P80T80t20 in Table 3). This indicates that HW prehydrolysis
is not necessary for the present methods. However, size reduction
processes, such as milling, may be desirable for achieving a high
degree of delignification.
TABLE-US-00002 TABLE 3 Chemical compositions of p-TsOH fractionated
(at P80T80t20) NE222 wood chips with and without hot-water
prehydrolysis and/or milling for dissolving pulp production. The
numbers in the parentheses are component yields. Solids yield
Glucan Xylan Mannan Lignin NE222.sup.1 (%) (%) (%) (%) (%)
Untreated 100.0 46.5 15.4 4.5 23.7 HW 93.2 49.4 (98.9) 7.1 (43.2)
1.6 (33.6) 25.6 (100.0) P80T80t20 75.6 60.4 (98.2) 7.3 (35.7) 2.8
(48.0) 18.6 (59.1) HW + P80T80t20 75.3 60.5 (97.9) 6.1 (29.8) 2.3
(38.5) 20.0 (63.5) Mill + P80T80t20 56.9 71.9 (87.9) 4.4 (16.4) 3.1
(39.5) 10.8 (14.2) HW + Mill + P80T80t20 54.2 73.4 (85.6) 4.2
(14.7) 3.0 (36.8) 5.3 (12.0) HW + P80T80t20 + Bleach 51.0 84.5
(92.7) 4.5 (14.9) 2.3 (26.0) 1.0 (2.0) Mill + P80T80t20 + Bleach
43.1 90.0 (83.4) 4.2 (11.8) 2.4 (22.7) 0.2 (0.3) HW + Mill +
P80T80t20 + Bleach 41.4 92.9 (82.6) 3.6 (9.6) 2.2 (20.5) 0.2 (0.3)
.sup.1HW stands for hot-water at 170.degree. C. for 50 min. (Pxx,
Txx, txx) stands for p-TsOH concentration in wt %, reaction
temperature in .degree. C. and reaction duration in min.
Chlorite bleaching was applied to three p-TsOH (P80T80t20)
fractionated solid samples: with HW only, with milling only, and
with both HW and milling as listed in Tables 4 and 5. Bleaching
entailed mixing 2 g dried solid sample, 65 mL of 75.degree. C.
DI-water, 0.5 mL of glacial acetic acid and 0.6 g of sodium
chlorite in a beaker for 4 hours. Additional reagents, consisting
of 0.5 ml of glacial acetic acid and 0.6 g of sodium chlorite, were
added at 1, 2 and 3 hours. The resulting bleached pulp was washed
by vacuum filtration with DI-water until the pH of the filtrate was
close to neutral, and then dried at 105.degree. C. The sample
without milling (HW+P80T80t20+Bleach) contained a substantial
amount of lignin, so the bleaching was repeated on a new sample
using double quantities of sodium chlorite, which resulted in a
relatively low lignin level. The two samples with milling had
relatively low xylan contents of approximately 4% or less, and
lignin contents of 0.2% after bleaching. The pulp viscosities of
these three samples were between 360 and 430 (mL/g), as listed in
Table 4, and are slightly lower than the range of 450-500 (mL/g)
for typical dissolving pulp fibers. Careful examination of the data
in Table 1 of FIGS. 38A and 38B, shows that a low reaction
temperature can result in low glucan degradation, or less
deploymerization of cellulose, which can be used to improve the
viscosity of the resultant pulp. The reduced delignification, due
to a lower temperature or low p-TsOH concentration, can be
compensated for by using a longer reaction time such as 60 min
(comparing P75T80t20 with P75T65t60).
TABLE-US-00003 TABLE 4 Bleached pulp viscosity and DP. Intrinsic
viscosity NE222 (mL/g) DP HW + P80T80t20 + Bleach 427.5 .+-. 0.7
587.6 .+-. 1.1 Mill + P80T80t20 + Bleach 377.7 .+-. 0.5 512.4 .+-.
0.9 HW + Mill + P80T80t20 + Bleach 357.5 .+-. 0.7 482.1 .+-.
0.4
Another set of experiments was carried out to evaluate the
feasibility of reducing acid concentration for dissolving pulp
production using the same refined poplar fibers described above
without HW pretreatment. As can be clearly seen from Table 5, a low
p-TsOH concentration can be compensated for with a longer reaction.
Both the pulp viscosity and xylan content after chlorite bleaching
are suitable for dissolving pulp.
TABLE-US-00004 TABLE 5 Chemical composition and pulp viscosity of
bleached poplar NE222 pulp delignified by p-TsOH. Solids Sample
yield Viscosity Glucan Xylan Mannan Lignin Label.sup.1 (%) (mL/g)
(%) (%) (%) (%) Poplar 45.7 14.9 4.6 23.4 NE222 P85T80t20 64.7 70.3
5.7 3.2 8.8 (post- 45.2 442 75.7 5.8 3.3 0.8 bleaching) P65T80t180
60.7 71.4 4.3 3.0 12.4 (post- 43.7 522 74.8 4.7 3.6 0.7 bleaching)
.sup.1(Pxx, Txx, txx) stands for p-TsOH concentration in wt %,
reaction temperature in .degree. C. and reaction duration in
min.
Example 6: Production of Dissolving Pulp from Birch Wood
To further evaluate p-TsOH fractionation for dissolving pulp
production, birch wood chips were used that are used widely for
pulp production and contained a minimal level of mannan. Medium
density fiberboard (MDF) type fibers were produced from the birch
wood chips in a 12'' pressurized disk refiner (Sprout-Bauer, model
1210P, Muncy, Pa., USA) by pre-steaming the wood chips at
165.degree. C. or steam pressure 0.62 MPa (105 Psia). The disk
plate pattern was D2B505 with a gap of 7/1000 inches. The wood chip
feeding rate was approximately 1 kg/min. The MDF process has three
distinct features uniquely suited, for this study: (1) low energy
cost in fiberization by pre-steaming above the lignin glass
transition temperature to initiate fiber separation in the middle
lamella; (2) as a result, a major portion of the lignin is exposed
on the resulting fiber surface, which should facilitate
solubilization of lignin by p-TsOH; (3) minimal fiber cutting that
can avoid unnecessary reduction of DP or pulp viscosity.
TABLE-US-00005 TABLE 6 Chemical compositions of p-TsOH fractionated
birch MDF for dissolving pulp and LCNF production. The numbers in
the parentheses are component yields (g/100 g wood). Solids yield
Glucan Xylan Mannan Lignin Birch MDF .sup.1 (%) (%) (%) (%) (%)
Untreated 100.0 38.7 .+-. 0.88 21.5 .+-. 0.02 1.9 .+-. 0.03 20.2
.+-. 0.67 P50T80t20 56.66 59.2 .+-. 0.96 15.0 .+-. 0.28 2.4 .+-.
0.02 16.0 .+-. 0.47 (33.6) (8.5) (1.3) (9.0) P65T80t20 54.15 62.0
.+-. 0.74 14.0 .+-. 0.12 2.6 .+-. 0.01 11.6 .+-. 0.32 (33.6) (7.6)
(1.4) (6.3) P75T80t20 53.76 65.3 .+-. 1.59 12.6 .+-. 0.21 2.3 .+-.
0.11 9.5 .+-. 0.23 (35.1) (6.7) (1.2) (5.1) P80T80t20 51.31 67.7
.+-. 0.20 12.2 .+-. 0.08 2.50 .+-. 0.07 7.2 .+-. 0.18 (34.7) (6.2)
(1.3) (3.7) P85T80t20 52.39 67.6 .+-. 2.69 11.2 .+-. 0.43 2.2 .+-.
0.10 8.0 .+-. 0.12 (35.4) (5.8) (1.2) (4.2) P80T65t60 53.12 65.9
.+-. 0.01 13.3 .+-. 0.02 2.9 .+-. 0.01 9.1 .+-. 0.03 (35.0) (7.1)
(1.5) (4.8) P80T65t60- 46.63 77.9 .+-. 2.07 13.6 .+-. 0.38 2.7 .+-.
0.26 1.1 .+-. 0.06 bleached
The washed fractionated solids of P80T65t60 were used for
dissolving pulp production. It appeared that the hydrolysis time of
60 min was too short when the temperature was reduced to 65.degree.
C. resulting in a hydrolyzed sample with very high xylan and lignin
content of over 13 and 9%, respectively. After bleaching, the
sample still had an undesirably high xylan content, while lignin
was reduced to approximately 1%. The viscosity of the bleached pulp
was 392 mL/g with DP of 533. The xylan in the sample contributed to
the low DP. A long reaction time would address the problem
associated with high lignin and xylan contents as shown in Table
5.
Example 7: Production of Lignocellulosic Nanocrystals from Birch
Wood
The MDF fibers described in example 6 were used for the integrated
production of LCNCs with LCNFs or LCMFs (depending on the extent of
mechanical fibrillation and the severity of p-TsOH treatment). The
MDF fibers were first fractionated using p-TsOH at several
conditions using a fiber to acid solution ratio of 1:10. These
conditions produced fractionated solids with varying lignin
contents, as listed in Table 6. The hydrolyzed solids were
thoroughly washed and centrifuged. The washed samples were dialyzed
to separate LCNCs from the partially hydrolyzed LCSR. At neutral pH
with conductivity between 1-2 .mu.S/cm, the supernatant through
centrifugation became turbid, suggesting the presence of LCNCs. The
supernatant was then removed and further diluted to 0.01% for AFM
imaging. As an example, the thoroughly washed hydrolyzed samples
from P85T80t20, P80T80t20, P65T80t20 were dialyzed. The separated
LCNC particles were fairly well dispersed, as shown by the AFM
images in FIGS. 4A, 4B, and 4C. The AFM height measured
distributions are shown in FIG. 5 with an average height of 26, 28,
and 51 nm, respectively. The bimodal distribution of sample
P85T80t20 was due to the free lignin nanoparticles as shown in FIG.
4A. The AFM images (FIGS. 4A-4C) showed very interesting morphology
of the LCNCs with very long lengths of over 1 .mu.m. The great
height and long length indicated that the resultant material was
CNC bundles.
Example 8: Production of Lignocellulosic Nanofibrils from Birch
Wood
The LCSR, after separating LCNCs from the washed hydrolyzed WIS,
was subsequently mechanically fibrillated to produce LCNFs or
LCMFs, depending on the extent of fibrillation and the severity of
acid hydrolysis. Optionally, especially under low-severity
hydrolysis conditions for producing long and entangled LCNFs, LCNCs
yield was low and the washed solids could be directly used for LCNF
production without dialysis and separating LCNCs. The LCSR, or
washed hydrolyzed WIS without separating LCNCs, was diluted with
water to 1% suspensions and fibrillated using a microfluidizer
(M-110EH, Microfluidics Corp., Westwood, Mass.). The suspensions
were initially processed through a 200 .mu.m chamber 3 times at 40
MPa, and then passed an additional 1-9 times through an 87 .mu.m
chamber at 120 MPa. Gelation was observed, suggesting that the
solid suspensions became nanofibrils. Atomic Force Microscopy (AFM)
images confirmed this as shown in FIGS. 6A, 6B, and 6C. These
samples were produced using LCSR from P50T80t20, P65T80t20, and
P80T80t20 after 5 passes through the 87 .mu.m chamber,
respectively. AFM measured fibril height probability density
distributions from these three samples are shown in FIG. 7. The
corresponding average heights of these three LCNF samples were
51.1, 29.4, 15.3 nm. All three LCNF samples showed remarkable
uniformity in height as indicated by the narrow distributions (FIG.
7). The LCNF with the highest lignin content contained lignin
nanoparticles (LNPs) clearly visible from the AFM image (FIG. 6).
Increased fractionation severity clearly reduced lignin content
(Table 6) and resulted in finer fibrils through mechanical
fibrillation.
Increasing the extent of fibrillation also resulted in LCNFs with
thinner diameters and less entanglement. The LCSR from the lowest
severity run P50T80t20 was fibrillated using different passes. AFM
measured fibril height distributions clearly showed the thinning of
the fibril with more passes (FIGS. 8A, 8B, 8C, 8D, and 8E). The
mean LCNF height was reduced from 70 to, 65.2, 51.1, 22.5, 14.3 nm
after increasing the numbers of passes through the 87 .mu.m chamber
of the microfluidizer from 1 to, 3, 5, 7, and 9 (FIG. 9),
respectively. Furthermore, the LCNFs became more uniform with more
fibrillation.
Example 9: Production of Lignocellulosic Nanofibrils from Ponderosa
Pine
Ponderosa pine, a softwood, was also used to produce LCNFs.
Ponderosa pine MDF fibers were produced with chips from Yreka,
Calif. using the same 12'' pressurized disk refiner and under the
same conditions as described in Example 6. The MDF fibers were then
treated using a p-TSOH solution of 80 wt % concentration at
80.degree. C. for 20 min, or P80T80t20. The acid hydrolyzed sample
was washed and 100 g in an oven dry (OD) base of the washed sample
was processed in a Supermasscolloider (Model: MKZA6-2, Disk Model:
MKGA6-80#, Masuko Sangyo Co., Ltd, Japan). The milling consistency
was 2%, and the time was 60 min in the Supermasscollioder (SMC). As
shown in FIG. 10, whisker-like cellulose nanofibrils were obtained.
Unlike microfluidization, however, SMC produced a non-uniform
cellulose nanofibril distribution, as indicated by the presence of
the long fibrils shown in FIGS. 10A and 10B. However, when the SMC
samples were subjected to two passes of microfluidization, all
particles became very short whisker-like material as shown in FIG.
11.
Example 10: Production of Lignin Nanoparticles from Spent
Liquor
The results in Tables 1 and 2 demonstrated that a substantial
amount of wood lignin was solubilized, especially for poplar NE222
(hardwood). It was found that the solubilized lignin could be
precipitated after diluting the aqueous spent liquor with
additional water because p-TsOH is a hydrotrope. The critical acid
concentration at which lignin precipitation occurred was monitored
by dynamic light scattering (DLS) using a zeta potential analyzer
(Nanobrook Omni, Brookhaven Instruments, Holtsville, N.Y.). The
results from precipitating spent liquor of poplar NE222 at
P75T80t20 are presented here. The DLS measured effective lignin
particle sizes in the spent liquor at different dilution ratios, or
equivalently the p-TsOH concentrations, are shown in FIG. 12. The
results show that lignin precipitation was minimal at p-TsOH
concentration .gtoreq.15%, as indicated by the very small measured
particle size of less than 300 nm, as well as the minimal increase
in size with dilution from the initial high concentration. The
measured particle size rapidly increased to approximately 3000 nm
when the spent liquor was diluted to a 10% concentration. The
increase in particle size was not substantial with further dilution
to below 4% concentration.
The spent liquor samples at the different dilution ratios were
centrifuged at 3000 g for 10 min. Lignin precipitation was minimal
at p-TsOH concentration of 20 wt % and higher. Precipitation
increased substantially with dilution and the supernatant changed
from highly opaque to clear. Therefore, the solubilized lignin
could be readily recovered simply through dilution with water. The
lignin recovery yield varied with dilution ratio. These results
indicate that near full recovery can be achieved at p-TsOH
concentration of approximately 4%.
Early studies on hydrotropes (Balasubramanian et al. 1989;
Hatzopoulos et al. 2011) indicated the existence of a minimal
hydrotrope concentration (MHC), also called critical aggregate
concentration (CAC), where hydrotropy is exhibited, i.e., below MHC
lignin solubility disappears. Conductivity measurements were used
for estimating the MHC. As shown in FIG. 13, the transition point
in the measured conductivity of the diluted p-TsOH aqueous solution
was at 11.5 wt %, suggesting MHC or CAC=11.5 wt %. This means that
when the concentrated p-TsOH solution was diluted below 11.5 wt %,
self-association disappeared. The solubility of lignin in the
solution was impaired, resulting in precipitation.
Example 11: Characterization of Lignin Nanoparticle Size
The spent liquor at 40 wt % from dissolving poplar wood at
P75T80t20 was diluted to 10 wt %, below the p-TsOH minimal
hydrotrope concentration of 11.5 wt %. 10 mL of the diluted spent
liquor was centrifuged at 3000 g for 10 min to precipitate the
dissolved lignin. 7.5 mL of DI water was added back to further
dilute the spent liquor to p-TsOH concentration of approximately 2
wt %. Almost all dissolved lignin was precipitated through
centrifugation. This was due to the strong ionic strength, which
compressed the double electric layer on the surface of suspended
lignin particles, making the lignin particles aggregate to
precipitate out under the centrifugation force. Most of the ions
were removed through further centrifugation and removing
supernatant (or acid) followed by dilution, which resulted in a
suspension with a p-TsOH concentration of 0.4 wt %, centrifugation
with 3000 g for 10 min was unable to precipitate the charge
particles due to the strong electrostatic repulsions among them,
resulting in a turbid supernatant. This turbid supernatant
exhibited a significant Tyndall effect; i.e., a red laser beam was
visible in the direction perpendicular to its incident direction
due to light scattering of very small particles. This showed that
the dispersion was an aqueous sol, or colloidal system, that
contained nanoparticles of lignin or LNPs.
The turbid supernatant and precipitate after the third centrifuge
step were thoroughly mixed back together to examine all the lignin
particles in the diluted spent liquor. An AFM topographic image of
the resultant whole diluted suspension deposited on a fresh mica
sheet is shown in the FIG. 14. The image confirmed nanoscale lignin
particles formed through self-assembly of dissolved lignin after
dilution. The sizes of the lignin nanoparticles ranged from 100 nm
to 1 micrometer. Aggregates could be observed as shown by the
multiple peaks in profile 1 in FIG. 15 corresponding to line 1 in
FIG. 14. Less aggregated particles are observed from AFM height
scanning profiles indicated by the separated single peaks in
profile 2 (dashed line in FIG. 15), which correspond to line 2 in
FIG. 14; and the diameter and thickness were determined to be
approximately 500 and 50 nm, respectively. This suggests that the
resultant LNPs were oblate spheroids.
The mixed diluted spent liquor was centrifuged at different speeds,
after which the turbid supernatant was examined by AFM. Larger
particles were precipitated during centrifugation, while only
smaller particles remained in the supernatant. After air drying the
supernatant on a mica plate, the sample obtained from
centrifugation at 3000 g for 10 min contained lignin particle
aggregates with lateral size of approximately 600 nm, as shown in
FIG. 16A. Increasing centrifuge speed to 10000 g or higher, removed
additional aggregates and large particles, resulting in relatively
uniform and small LNPs in the supernatant as shown in FIGS. 16B and
16C. Typical LNP lateral sizes are approximately 200 and 50 nm at
10000 g and 15000 g, respectively. These results indicate that the
diluted spent acid liquor contained lignin particles from tens of
nanometers to approximately 1 micron. Furthermore, the large
particles can be separated through centrifugation. AFM height
measurements of the three supernatant samples are presented in FIG.
17. The heights are much smaller than their lateral dimensions.
This shows that the LNPs were oblate spheroid nanoparticles with
aspect-ratios (lateral or diameter:heights or thickness) of
approximately 20, based on the results presented in FIGS. 16 and
17.
Example 12: Control of Lignin Nanoparticle Size and Surface
Charge
Particle charge is a critical property to particle dispersion and
colloidal characteristics. The spent liquor from P75T80t20 at 40 wt
% was quickly diluted to 10 wt % and then dialyzed to approximately
pH 4.5. The average zeta-potential of the LNPs in the dialyzed
sample was approximately -30 mV. Centrifugation can remove large
particles in a suspension resulting in a supernatant that contains
smaller particles, as discussed previously. This is clearly shown
in FIG. 18 as measured by DLS of the LNPs in the diluted spent acid
liquor. Removing large particles may also have facilitated particle
dispersion in water, since the zeta potential increases from
approximately -30 mV to -45 mV for the remaining LNPs in the
supernatant after removing large particles using centrifugation at
3000 g (or higher) for 10 min (FIG. 18).
The speed of dilution was found to affect LNP morphology. 5 g of
the spent liquor at a p-TsOH concentration of 40% from the run
P75T80t20 was mixed with 15 g DI water using a peristaltic pump at
four different flow rates of 0.19, 0.95, 2.85 and 5.71 mL/min,
respectively. The dilution speed was determined in terms of
dilution times/min. An extremely fast dilution speed of 240
times/min was achieved by manually adding 15 g of water into the
flask in 1 second. A final dilution ratio of 4 times was applied in
all dilution experiments to p-TsOH concentration of 10 wt %. The
dissolved lignin aggregates when the spent liquor is diluted to 10
wt % (below the MHC of 11.5 wt %). The speed of dilution or water
mixing with the hydrotrope p-TsOH during dilution affected lignin
aggregation and dispersion. DLS measured LNP size decreased rapidly
from approximately 900 nm, when the spent acid liquor was diluted
to 10 wt % at the slowest rate, to 450 nm when diluted at the
fastest rate, as shown in FIG. 19A. The DLS measured particle sizes
were also qualitatively in agreement with the lateral diameters
from AFM images (FIGS. 20A, 20B, and 20C). The increase in particle
size was a direct result of dissolved lignin aggregation during
dilution. Apparently, a slow dilution increased the dissolved
lignin aggregation time and resulted in a larger DLS particle size
than that obtained via a fast dilution. A longer aggregation time
also resulted in the increase in the thickness of lignin
aggregates, as confirmed by the AFM measured height distributions
(FIG. 19B).
For negatively charged LNPs, pH and ionic strength can affect their
aggregation and charge. The effects of pH were investigated by
spiking a solution of NaOH at 0.1 mol/L or with HCl at 0.1 mol/L
into the lignin supernatant from centrifuging at 3000 g for 10 min
and subsequently dialyzing to pH 4.5. DLS measured LNP mean
particle sizes were relatively stable between pH 3.0-10 with a
slight reduction in size as pH increased to approximately 7.5,
followed by a slight size increase as the pH increased to 10, as
shown in FIG. 21A. Reducing pH below 3 or increasing pH above 10
resulted in a rapid increase in DLS measured LNP size. This was
also verified by AFM imaging as shown in FIGS. 22A, 22B, and 22C.
The results shown in FIG. 21A show that pH is a good parameter to
control LNP size. Furthermore, within a wide range of pH 3-10, mean
DLS LNP size was fairly constant. This is important for LNP
applications.
Zeta potential shows the opposite trend of LNP size with respect to
pH. With increasing pH, the zeta potential increased (absolute
value) rapidly from about -4 mV to approximately -50 mV at about pH
8, and then decreased rapidly as the pH rose to near 12. The
maximal zeta potential corresponded closely to the smallest LNP
size (FIG. 21A), showing that electrostatic repulsion played a
major role in lignin particle aggregation. The results also
indicated that a zeta potential of -25 mV or higher (absolute
value) was desirable to avoid substantial lignin particle
aggregation, as shown by the rapid increase in LNP size at zeta
potential below 25 mV.
The result of the dilution experiments showed that ionic strength
affected colloidal suspension precipitation behavior by affecting
the double electric layer surrounding the LNP surface. The effect
of ionic strength on LNP size was evaluated by spiking a NaCl
solution into a dialyzed LNP suspension of pH 6.4. As the
concentration of NaCl was increased to 20 mM, the zeta-potential of
the LNP was decreased (in absolute value) from approximately -50 mV
to -25 mV, at which point there was a rapid increase in particle
size due to aggregation, as shown in FIG. 23A. This critical
zeta-potential of -25 mV is in agreement with that observed in the
pH effect study (FIG. 21A). The aggregation phenomenon is clearly
shown by AFM imaging, as shown in FIGS. 24A, 24B, and 24C as well
as AFM measured height distributions (FIG. 23B).
Fractionation conditions also affected the LNP size. As listed in
Table 7, more severe reaction conditions resulted in a larger LNP
particle size for both NE222 and Douglas-fir. In addition, more
severe reaction conditions often resulted in increased dissolution
of lignin. The amount of lignin dissolved and DLS measured LNP size
were correlated as shown in FIG. 25 (NE222). More lignin
dissolution resulted in a higher LNP concentration in the diluted
spent liquor at 10 wt %. A higher lignin concentration certainly
could have increased aggregation, simply due to the increased
collision probability among lignin particles. The amount of lignin
dissolved in a spent liquor was determined from the lignin mass
balance by evaluating the residual lignin in the washed water
insoluble solids. As a verification, the amount of dissolved lignin
was also determined by diluting the spent liquor to 4% to fully
precipitate dissolved lignin. The precipitated lignin was then
washed thoroughly. The oven dry weight of the washed lignin was
measured gravimetrically for yield determination (listed in Table
7). Discrepancies existed between these two methods (Table 7),
perhaps due to losses in precipitation and washing.
TABLE-US-00006 TABLE 7 Lignin nanoparticles from different
treatment of poplar and Douglas fir measured from the spent acid
solution diluted to 10%. Biomass Treatment Lignin dissolved (%)
Diameter Zeta Potential Species Condition Solid Liquor nm mV NE222
P70T50t20 29.8 25.0 349.7 .+-. 1.5 -40.0 .+-. 0.2 P70T65t20 65.1
63.9 371.7 .+-. 8.4 -36.5 .+-. 0.2 P70T65t35 63.9 60.3 413.7 .+-.
2.1 -41.4 .+-. 1.0 P70T80t20 77.6 68.2 441.5 .+-. 4.2 -35.1 .+-.
0.3 P75T65t20 71.6 63.9 438.6 .+-. 5.1 -33.8 .+-. 0.7 P75T65t35
77.4 60.7 474.8 .+-. 3.2 -41.1 .+-. 1.2 P75T65t60 81.0 58.7 500.4
.+-. 1.6 -36.7 .+-. 2.2 P75T80t20 85.5 73.7 467.1 .+-. 2.5 -37.9
.+-. 3.6 P80T80t20 90.7 78.6 529.6 .+-. 7.4 -34.1 .+-. 1.3 Fir
P70T80t20 26.5 25.0 518.5 .+-. 4.6 -36.7 .+-. 0.9 P75T80t20 36.3
26.1 605.3 .+-. 17.9 -35.2 .+-. 0.7 P80T80t20 53.9 52.6 888.4 .+-.
122.7 -32.9 .+-. 0.5
Table 7 also indicates that LNPs from softwood have a much larger
size than that from poplar NE222. All LNPs from different
fractionation conditions have very high negative zeta potential as
listed in Table 7, indicating that all LNPs could be well dispersed
in liquids.
Example 13: Lignin Nanoparticle Size Stability
Colloidal stability of LNPs is important for a variety of
applications. The diluted p-TsOH spent liquor from P75T80t20 at 40
wt % was used to study LNP colloidal stability. The spent liquor
was further diluted to 10 wt %, then dialyzed to a pH of
approximately 4.5. The dialyzed LNP suspension was then centrifuged
at 3000 g for 10 min. The precipitated lignin from centrifugation
was re-suspended in DI water. The stabilities of the LNPs in the
supernatant from the centrifuge and in the suspension of
re-suspended precipitates were analyzed periodically using dynamic
light scattering (DLS) for a period of two weeks. Samples of each
suspension was first vigorously hand shaken each time before DLS
analyses. AFM images of each suspension at time zero and at the end
of two weeks were also taken. DLS analyses show that the DLS size
of the LNPs in the supernatant was slightly increased gradually
during a period of two weeks from approximately 310 nm to 370 nm
(FIG. 26). Over the same period, mean zeta-potential gradually
decreased from -28 mV to -11 mV (FIG. 27). AFM images obtained at
time 0 and after two weeks confirmed the increase in LNP size
(FIGS. 28A and 28B). The increase in LNP size was a direct result
of particle aggregation. This aggregation also increased the
particle thickness as shown by the AFM measured particle height
probability density (FIG. 29).
DLS-measured mean size of LNPs in the suspension of the
re-suspended precipitated lignin decreased over a period of two
weeks from 540 nm to 450 nm (FIG. 26). The resuspension of these
precipitated particles in DI water increased the pH of the
suspension, which resulted in a high surface charge (FIG. 27),
according to the results shown in FIGS. 21A and 21B, and prevented
aggregation during drying for AFM imaging. The AFM-measured
particle thickness measurements (FIG. 31) were qualitatively in
agreement with the DLS size measurements. FIG. 30A is an AFM image
of LNPs from a suspension of re-suspended precipitates. FIG. 30B is
an AFM image of LNPs in a supernatant from a centrifuge at t=0.
Example 14: p-TsOH-Based Delignification for Wood Fiber Production
Using Birch Wood
The birch MDF described in Example 6 was used to produce corrugated
medium fibers through p-TsOH-based lignocellulosic biomass
fractionation. Most of the data listed in Table 8 were obtained
from Example 6, but are presented in terms of component yields in
theoretical percentages as compared to mass-based component yields
in Table 6. Different degrees of delignification could be achieved
by varying reaction severity. The scale-up run T50P81t27, using 750
g in oven dry (OD) weight MDF, resulted in similar results as the
lab scale run T50P80t20. The scale-up run had slightly increased
delignification due to a slightly longer reaction time of 27 min
(including a 0.5*heat-up period of 14 min).
TABLE-US-00007 TABLE 8 Chemical compositions of p-TsOH fractionated
birch MDF samples under different conditions. The numbers in the
parentheses are component recovery yields theoretical percentages.
Solids yield Glucan Xylan Mannan Lignin Sample Label.sup.1 (%) (%)
(%) (%) (%) Untreated Birch 36.2 22.5 1.2 22.5 Birch MDF 100.0 34.6
20.8 1.9 23.0 P40T80t55 60.6 51.7 (90.5) 13.3 (38.8) 2.3 (73.7)
17.6 (46.4) P50T80t20 56.7 59.2 (97.0) 15.0 (40.8) 2.4 (70.8) 16.0
(39.3) P50T80t40 59.6 53.7 (92.4) 13.0 (37.3) 2.0 (63.5) 15.3
(39.5) P50T80t80 56.5 61.1 (99.8) 11.9 (30.9) 2.4 (72.5) 13.8
(34.0) P65T80t20 54.2 62.0 (97.0) 14.0 (36.4) 2.6 (74.9) 11.6
(27.4) P80T80t20 51.3 67.7 (100.4) 12.2 (30.0) 2.5 (68.2) 7.2
(16.0) P50T81t27.sup.2 52.8 57.7 (89.8) 14.7 (36.7) 2.7 (74.6) 15.1
(35.4) .sup.1(Pxx, Txx, txx) stands for p-TsOH concentration in wt
%, reaction temperature in .degree. C. and reaction duration in
min. .sup.2scale-up run at 750 g, average temperature.
Based on the amount of lignin removal from the lab bench scale run,
a targeted reaction condition of P50T80t20 was chosen for a
scale-up study to produce corrugated medium fibers. The actual
reaction condition P50T81t27 deviated slightly due to difficulties
in controlling the exact temperature using steam-jacket heating and
the increased heat-up period of the larger scale-up reactor. The
lignin content of the p-TsOH-based fractionation of the fibers was
15% (Table 8) after solubilizing 65% of the wood lignin. This
lignin content is about the same as that of typical corrugated
medium pulp fibers. The morphologies of the delignified fibers are
shown in FIG. 32B in comparison with the initial MDF fibers in FIG.
32A. Typical MDF fibers have a length over 2 mm, due mainly to the
presence of many fiber bundles. The p-TsOH treatment separated the
fiber bundles. The length of these separated fibers was over 1 mm.
Refining reduced fiber length, but improved fiber fibrillation, as
can be seen from the optical and scanning electronic microscopic
(SEM) images (FIGS. 33A and 33B).
Due to difficulties in making high basis weight sheets in the
laboratory, the initial studies on the mechanical properties are
from sheets with basis weight of 60 gm.sup.-2. The results indicate
that a tensile index of approximately 25 Nmg.sup.-1 was achieved
after refining to approximately 500 (mL) Canadian Standard Freeness
(CSF) (FIG. 34A). The failure strain is shown in FIG. 34B.
Example 15: p-TsOH-Based Fractionation of an Agricultural Residue:
Wheat Straw
Lightly hammer-milled wheat straw was fractionated directly using
concentrated p-TsOH solution in a range of conditions similar to
that described in Example 1. The wheat straw was first water washed
to remove dirt. Good selectivity in dissolving lignin over
cellulose was obtained, as listed in Table 9. At a relatively low
p-TsOH acid concentration of 40 w %, over 50% straw lignin
dissolved while over 85% of cellulose was retained. Wheat straw
usually contains a substantial amount of silicate, as can be seen
from the high ash content of 5.1% listed in Table 9 (obtained by
burning at 560.degree. C. the residual solids after a two-step
sulfuric acid hydrolysis of carbohydrates). It appears that
silicate was fully retained in the WIS after p-TsOH-based
lignocellulosic biomass fractionation. This is beneficial, as it
helps to increase the WIS yield for material production as well as
avoiding silicate-caused equipment corrosion problems in downstream
processing. The silicate can also improve the hydrophobicity of the
solids for LCNF or LCMF production.
TABLE-US-00008 TABLE 9 Chemical compositions of p-TsOH-based
fractionation of wheat straw samples under different conditions.
The numbers in the parentheses are component yields based on the
component in the untreated wheat straw. Solids yield Glucan Xylan
Ash K. Lignin Sample Label.sup.1 (%) (%) (%) (%) (%) Untreated 100
40.8 24.5 5.1 20.4 Wheat Straw P20T40t20 94.7 41.4 (95.9) 22.9
(88.3) 5.3 (97.7) 20.7 (96.2) P20T50t20 93.3 39.5 (90.2) 21.8
(82.8) 5.5 (100.4) 19.9 (91.2) P20T60t20 89.8 38.3 (84.2) 21.5
(78.5) 6.4 (111.9) 19.5 (85.9) P25T60t30 87.3 41.1 (88.0) 22.0
(78.3) 5.2 (87.7) 19.0 (81.7) P25T60t30R 87.3 41.7 (89.2) 22.9
(81.4) 6.1 (103.6) 19.8 (85.1) P35T60t30 80.5 43.2 (85.2) 20.5
(67.4) 8.2 (128.1) 20.7 (81.8) P35T60t60 75.5 45.4 (84.0) 17.9
(55.2) 7.1 (104.2) 19.1 (70.7) P40T70t60 67.1 48.3 (79.4) 14.9
(40.7) 9.0 (117.4) 17.8 (58.5) P40T80t60 66.0 54.7 (88.6) 13.4
(36.1) 8.9 (114.1) 16.9 (54.8) P40T80t60R 66.0 52.5 (84.9) 13.3
(35.9) 7.6 (97.2) 17.2 (55.8) P40T80t90 58.3 57.7 (80.4) 12.0
(27.9) 9.2 (104.0) 16.3 (46.8) P40T80t120 62.3 56.3 (88.1) 11.7
(30.5) 9.2 (111.8) 15.8 (48.4) P50T80t60 57.2 55.1 (77.1) 11.4
(26.5) 9.5 (105.5) 14.4 (40.5) P50T80t90 56.0 59.0 (80.9) 10.9
(24.9) 9.2 (99.8) 14.0 (38.6) P60T80t60 55.0 62.1 (83.8) 10.0
(22.4) 8.5 (91.2) 11.2 (30.3) P60T80t90 55.0 59.3 (79.9) 8.5 (19.1)
10.1 (108.4) 14.0 (37.9) .sup.1(Pxx, Txx, txx) stands for p-TsOH
concentration in wt %, reaction temperature in .degree. C. and
reaction duration in min. R stands for replicate fractionation run.
R stands for replicate fractionation run.
Example 16: p-TsOH-Based Fractionation of an Energy Crop:
Switchgrass
Mildly hammer-milled switchgrass was also fractionated using
concentrated p-TsOH solution in the range of conditions used for
the wheat straw in Example 14. The switchgrass was also washed and
air dried before use. Again, good selectivity of dissolved lignin
over cellulose was achieved. The relatively lower dissolution of
lignin of approximately 60% compared to 85% for wood described
previously was perhaps due to the relatively larger size of the
materials as well as the relatively low p-TsOH concentrations used
in the p-TsOH-based fractionation. Further hammer-milling the
switchgrass is expected to achieve improved dissolution of
lignin.
TABLE-US-00009 TABLE 10 Chemical compositions of p-TsOH-based
fractionation of switchgrass samples under different conditions.
The numbers in the parentheses are component yields based on the
component in the untreated switchgrass. Solids yield Glucan Xylan
K. Lignin Sample Label.sup.1 (%) (%) (%) (%) Untreated 100 37.3
26.1 23.5 Switchgrass P20T40t20 91.4 40.1 (98.2) 25.2 (88.5) 23.0
(89.5) P20T50t20 90.2 39.6 (95.7) 26.5 (91.6) 23.7 (91.0) P20T60t20
89.6 40.3 (96.9) 25.5 (87.6) 24.4 (93.2) P25T60t30 87.8 39.4 (92.7)
26.4 (88.9) 24.2 (90.5) P25T60t30R 87.8 40.7 (95.8) 25.6 (86.2)
23.1 (86.4) P35T60t30 83.4 41.7 (93.2) 25.4 (81.1) 24.8 (87.9)
P35T60t60 76.4 42.3 (86.6) 20.7 (60.7) 24.9 (81.2) P40T70t60 68.2
51.7 (94.5) 19.8 (51.8) 23.9 (69.4) P40T80t60 59.7 52.5 (83.9) 14.5
(33.2) 22.7 (57.6) P40T80t90 59.4 48.8 (94.4) 13.2 (30.0) 21.3
(53.9) P40T80t120 59.3 59.2 (78.6) 12.5 (28.4) 19.9 (50.3)
P50T80t60 57.4 49.4 (88.5) 13.5 (29.8) 20.7 (50.5) P50T80t90 55.1
57.5 (86.9) 13.5 (28.4) 19.0 (44.6) P60T80t60 55.1 58.9 (93.2) 12.0
(25.4) 19.6 (45.9) P60T80t90 52.9 63.1 (92.3) 11.1 (22.5) 18.7
(42.1) .sup.1(Pxx, Txx, txx) stands for p-TsOH concentration in wt
%, reaction temperature in .degree. C. and reaction duration in
min. R stands for replicate fractionation run. R stands for
replication fractionation runs.
Example 17: Solubilization of Commercial Technical Lignin Using an
Aqueous p-TsOH Solution
Commercial lignin is readily available but cannot be solubilized in
aqueous systems to produce micro or nanoparticles. Aqueous p-TsOH
was also used to solubilize commercial alkali technical lignin
purchased from Sigma-Aldrich (St. Louis, Mo.). At a given
temperature of 80.degree. C., alkali lignin was gradually added
into a 100 g of p-TsOH solution with stirring until the solution
could no longer solubilize lignin, as observed from precipitation.
The solubility was the maximal amount of lignin solubilized in the
100 g solution. As shown in FIG. 35A, lignin solubility at
80.degree. C. was increased with p-TsOH concentration. Solubility
increased rapidly at p-TsOH concentrations above 40 wt %, with a
solubility of 35 g/100 g at a p-TsOH concentration of 55 wt %.
Lignin solubility was also increased with temperature, as shown in
FIG. 35B, and reached a plateau at approximately 65.degree. C. at a
p-TsOH concentration of 50 wt %. The solubilized lignin was
separated through centrifugation after diluting the solution to 10
wt % with water to precipitate lignin. AFM images revealed that the
precipitated LNPs had a circular shape with a lateral diameter of
approximately 100-200 nm, as shown in FIGS. 36A, 36B, and 36C. The
AFM topographic measured heights indicated average heights were
approximately 4-6 nm, as shown in FIG. 37. Gel permeation
chromatography (GPC) molecular measurements indicated that Mw was
approximately 7000, as listed in Table 11, except for the run at a
severe condition of P55T80.
TABLE-US-00010 TABLE 11 GPC measured molecular weight of LNPs from
solubilizing alkali lignin in p-TsOH solutions Run Mn Mw PDI P40T35
1791 7480 4.18 P40T65 1812 7098 3.91 P50T65 1774 7282 4.10 P55T80
2130 11934 5.60
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The word "illustrative" is used herein to mean serving as an
example, instance, or illustration. Any aspect or design described
herein as "illustrative" is not necessarily to be construed as
preferred or advantageous over other aspects or designs. Further,
for the purposes of this disclosure and unless otherwise specified,
"a" or "an" means "one or more."
The foregoing description of illustrative embodiments of the
invention has been presented for purposes of illustration and of
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed, and modifications and
variations are possible in light of the above teachings or may be
acquired from practice of the invention. The embodiments were
chosen and described in order to explain the principles of the
invention and as practical applications of the invention to enable
one skilled in the art to utilize the invention in various
embodiments and with various modifications as suited to the
particular use contemplated. It is intended that the scope of the
invention be defined by the claims appended hereto and their
equivalents.
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